title: Nonequilibrium dynamics of helix reorganization observed by transient 2D IR spectroscopy.
abstract: The relaxation of helical structures very close to equilibrium is observed via transient 2D IR spectroscopy. An initial distribution of synthetically distorted helices having an unnatural bridge linking the 10th and 12th residues of an alanine-rich α-helix is released to evolve into the equilibrium distribution of α-helix conformations. The bridge constrains the structure to be slightly displaced from the full α-helix equilibrium near these residues, yet the peptide is not unfolded completely. The release is accomplished by a subpicosecond pulse of UV irradiation. The resulting 2D IR signals are used to obtain snapshots of the ∼100-ps helical conformational reorganization of the distorted dihedral angle and distance between amide units at chemical bond length-scale resolution. The decay rates of the angle between the dipoles, dihedral angles, and distance autocorrelations obtained from molecular dynamics simulations support the experiments, providing evidence that the final helix collapse conforms to linear response theory.
authors.affiliation: Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Tucker
authors.forename: Mohannad
authors.initials: M
authors.lastname: Abdo
authors.forename: Joel R
authors.initials: JR
authors.lastname: Courter
authors.forename: Jianxin
authors.initials: J
authors.lastname: Chen
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Brown
authors.forename: Amos B
authors.initials: AB
authors.lastname: Smith
authors.forename: Robin M
authors.initials: RM
authors.lastname: Hochstrasser
mesh_terms: D000595:Amino Acid Sequence; D007700:Kinetics; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000737:chemistry; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013055:Spectrophotometry, Infrared / Q000379:methods*; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D009842:Oligopeptides; D010455:Peptides
keywords: helix dynamics; synthetic peptides; tetrazines